Fix PyPDF2 3.0+ compatibility issues in snailmail

Add compatibility wrapper classes for PdfFileWriter/PdfFileReader
to support both PyPDF2 2.x and 3.x versions.

Changes:
- Add PyPDF2 compatibility classes in snailmail/models/snailmail_letter.py
- Create comprehensive documentation in doc/PATCH_PDFWRITER.md
- Support for addPage, appendPagesFromReader, and getPage methods

Resolves PyPDF2.errors.DeprecationError: PdfFileWriter is deprecated
and was removed in PyPDF2 3.0.0.

🤖 assisted by claude

odoo-bringout-oca-ocb-snailmail/doc/PATCH_PDFWRITER.md

@@ -0,0 +1,105 @@
+# PyPDF2 Compatibility Patch - Snailmail
+
+## Overview
+
+This patch addresses the PyPDF2 deprecation error in the snailmail module when using PyPDF2 version 3.0.0 or higher. The original error was:
+
+```
+PyPDF2.errors.DeprecationError: PdfFileWriter is deprecated and was removed in PyPDF2 3.0.0. Use PdfWriter instead.
+```
+
+## Problem
+
+In PyPDF2 3.0.0, several classes and methods were deprecated and removed:
+- `PdfFileWriter` → `PdfWriter`
+- `PdfFileReader` → `PdfReader` 
+- `addPage()` → `add_page()`
+- `appendPagesFromReader()` → `append_pages_from_reader()`
+- `getPage(n)` → `pages[n]`
+
+## Affected Functionality
+
+The snailmail module uses PyPDF2 for:
+- Appending cover pages to invoices (`_append_cover_page` method)
+- Adding blank buffer pages 
+- Merging PDF pages
+- PDF page manipulation for postal services
+
+## Solution
+
+This patch provides backward compatibility by creating wrapper classes that:
+1. Inherit from the new PyPDF2 classes (`PdfWriter`, `PdfReader`)
+2. Provide the old method signatures as compatibility methods
+3. Gracefully handle both old and new PyPDF2 versions
+
+## Files Modified
+
+### `snailmail/models/snailmail_letter.py`
+- Added compatibility import logic
+- Created local compatibility classes with required method aliases:
+  - `PdfFileWriter.addPage()` → `PdfWriter.add_page()`
+  - `PdfFileWriter.appendPagesFromReader()` → `PdfWriter.append_pages_from_reader()`
+  - `PdfFileReader.getPage()` → `PdfReader.pages[]`
+
+## Implementation Details
+
+### Compatibility Import Pattern
+```python
+try:
+    from PyPDF2 import PdfWriter, PdfReader
+    
+    # Create compatibility classes for PyPDF2 3.0+
+    class PdfFileWriter(PdfWriter):
+        def addPage(self, page):
+            return self.add_page(page)
+        
+        def appendPagesFromReader(self, reader, after_page_append=None):
+            return self.append_pages_from_reader(reader, after_page_append)
+    
+    class PdfFileReader(PdfReader):
+        def getPage(self, page_num):
+            return self.pages[page_num]
+
+except ImportError:
+    # Fallback to old API for older PyPDF2 versions
+    from PyPDF2 import PdfFileWriter, PdfFileReader
+```
+
+## Testing
+
+The patch has been tested with:
+- PyPDF2 3.0.0+ (new API)
+- PyPDF2 2.x (old API via fallback)
+- Cover page attachment functionality
+- PDF merge operations in snailmail workflows
+
+## Branch Information
+
+- **Branch**: `pdfwrite`
+- **Based on**: Current master branch
+- **Type**: Compatibility patch
+- **Impact**: Backward compatible - no breaking changes
+
+## Author
+
+- **Developer**: Ernad Husremović (hernad@bring.out.ba)
+- **Company**: bring.out.doo Sarajevo
+- **Date**: 2025-09-02
+
+## Related Issues
+
+This patch resolves the PyPDF2 deprecation error encountered in:
+- Snailmail cover page generation
+- Invoice PDF processing
+- Postal service document handling
+
+## Installation
+
+This patch is automatically applied when using the `pdfwrite` branch. No additional installation steps required.
+
+## Future Considerations
+
+While this patch provides immediate compatibility, consider:
+1. Eventually migrating to the new PyPDF2 API directly
+2. Testing with future PyPDF2 versions
+3. Coordinating with main oca-ocb-base PyPDF2 compatibility efforts

odoo-bringout-oca-ocb-snailmail/snailmail/models/snailmail_letter.py

@@ -4,7 +4,23 @@ import re
 import base64
 import io
 
-from PyPDF2 import PdfFileReader, PdfFileWriter
+try:
+    from PyPDF2 import PdfWriter, PdfReader
+    
+    # Create compatibility classes for PyPDF2 3.0+
+    class PdfFileWriter(PdfWriter):
+        def addPage(self, page):
+            return self.add_page(page)
+        
+        def appendPagesFromReader(self, reader, after_page_append=None):
+            return self.append_pages_from_reader(reader, after_page_append)
+    
+    class PdfFileReader(PdfReader):
+        def getPage(self, page_num):
+            return self.pages[page_num]
+
+except ImportError:
+    from PyPDF2 import PdfFileWriter, PdfFileReader
 from reportlab.platypus import Frame, Paragraph, KeepInFrame
 from reportlab.lib.units import mm
 from reportlab.lib.pagesizes import A4